Reactions of polycyclic thioketones with a phosphonylated carbanion

Abstract

Polycyclic, nonenolizable cycloaliphatic thioketones 1a and 1b react smoothly with the lithium salt of diethyl methylphosphonate 7 in THF solution at −40°C to afford products of the carbophilic attack exclusively. Quenching of the obtained lithium thiolates with alkyl iodides yields sulfanes of type 9 or 11, respectively, in good yields. 1‐Fluoro‐2,4‐dinitrobenzene was shown to act as an arylating agent. In the case of the “cage” thioketone 1b, the carbanion of salt 7 approaches the CS bond from the exo‐side exclusively. In contrast to the parent carbonyl compounds, thioketones 1 show no tendency to undergo the conversion analogous to the Horner–Wadsworth–Emmons reaction, which would result in the formation of an olefinic product. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:182–187, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20390

Reactions of Cycloaliphatic Thioketones and Their Oxo Analogues with Lithiated Methoxyallene: A New Approach to Vinylthiiranes

“…It is known that nucleophiles attack the C=S or C=O unit of Cooksons "birdcage" compounds exclusively from the exo-face. [11,17] Therefore, the two isomers are generated during the 1,3-cyclization of the intermediate thiol 20, affording the mixture of cis-21 and trans-21 in 71 % combined yield (Scheme 7). Attempted separation led to isolation of a small sample of the major isomer as an oil; however, an unequivocal assignment of the configuration of the two isomers was not possible.…”

“…The reaction was carried out in analogous manner, and the 1 H NMR spectroscopic analysis of the crude product showed the presence of two diastereomeric thiiranes in which the signals of two methoxy groups were found at 3.40 and 3.38 ppm (ratio 61:39). It is known that nucleophiles attack the CS or CO unit of Cookson’s “birdcage” compounds exclusively from the exo ‐face 11. 17 Therefore, the two isomers are generated during the 1,3‐cyclization of the intermediate thiol 20 , affording the mixture of cis ‐ 21 and trans ‐ 21 in 71 % combined yield (Scheme ).…”

“…Addition of lithiated methylphosphonate 6 to cycloaliphatic thioketones 1 a and 1 b furnished products 7 a and 7 b , respectively, as a result of carbophilic attack (Scheme ). The intermediate thiolate anions were trapped in both examples with 1‐chloro‐2,4‐dinitrobenzene to give the corresponding thioethers 11. Similarly, additions of carbanions, generated from esters and nitriles by treatment with lithium diisopropylamide, to the CS bond of 1 a results in the exclusive formation of thiol derivatives as the products of reactions with the thioketone carbon atom 12.…”

“…The intermediate thiolate anions were trapped in both examples with 1-chloro-2,4-dinitrobenzene to give the corresponding thioethers. [11] Similarly, additions of carbanions, generated from esters and nitriles by treatment with lithium diisopropylamide, to the C=S bond of 1 a results in the exclusive formation of thiol derivatives as the products of reactions with the thioketone carbon atom. [12] Apparently, carbanions stabilized by electron-withdrawing substituents such as enolates strongly prefer the carbophilic attack.…”